Bash – What Does [ -t 1 ] Check?

bashshelltestzsh

I just found a way to start zsh when I start the bash on Windows from

https://www.howtogeek.com/258518/how-to-use-zsh-or-another-shell-in-windows-10/.

It recommended to add following code at the last of .bashrc.

# Launch Zsh
if [ -t 1 ]; then
exec zsh
fi

What does [ -t 1 ] mean?

Is it just true?

Then, can I just do this?

exec zsh

Best Answer

[] is shortcut of test command.

According to man test:

-t FD
True if FD is a file descriptor that is associated with a terminal.

So if you running bash as interactive shell (terminal - see this thread for terminology explanation), bash will be replaced by zsh.

More about .bash* files:

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.

When a login shell exits, bash reads and executes commands from the files ~/.bash_logout and /etc/bash.bash_logout, if the files exists.

When an interactive shell that is not a login shell is started, bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of ~/.bashrc.

Stéphane Chazelas comment:
Note that a shell can be interactive without stdout being a terminal, and a shell can be non-interactive with a terminal on stdout (like anytime you run a script within a terminal without redirecting/piping its output), and bash can read .bashrc even when not interactive (like in ssh host cmd where bash is the login shell of the user on host, or bash --login -c 'some code'). case $- in *i*)... is the correct way to test if a shell is interactive.

Related Solutions

Bash – What does : ${param:=value} mean

Let's break this down into pieces.

This code runs the command : with some arguments. The command : does nothing and ignores its arguments. Therefore the whole command line does nothing, except whatever side effects happen in the arguments.

The syntax ${parameter_name:=value} exists in all non-antique Bourne-style shells, including ash, bash, ksh and zsh. It sets the parameter to a default if necessary. It is equivalent to

if [ -z "$parameter_name" ]; then parameter_name=value; fi
… ${parameter_name}

In other words, if parameter_name is not set or is set to an empty value, then set it to the indicated value; and then run the command, using the new parameter value. There is a variant, ${parameter_name=value}, which leaves the parameter empty if it was empty, only using the indicated value if the parameter was unset.

You'll find this syntax documented under “parameter expansion” in the POSIX spec, and the dash, bash, ksh and zsh manuals.

There are variations on this syntax, in particular ${parameter_name:-value} which let you use a default value for this expansion only, without assigning to the parameter.

In summary, : ${parameter_name:=value} is a concise way of writing

if [ -z "$parameter_name" ]; then parameter_name=value; fi

Zsh !! and !$ auto execute as it does in bash

From man zshoptions

HIST_VERIFY
    Whenever the user enters a line with history expansion,  don't  execute  the  line
    directly;  instead, perform history expansion and reload the line into the editing buffer.

To disable this option run setopt no_hist_verify. You can also have a look at your config file and remove the hist_verify option or just explicitly disable it.

Best Answer

Related Solutions

Bash – What does : ${param:=value} mean

Zsh !! and !$ auto execute as it does in bash

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